Understanding Bicarbonate Levels for Student Nurses
Learn what bicarbonate means on a blood test or blood gas, how it contributes to acid-base balance and why the result should always be interpreted alongside pH, carbon dioxide and the patient's condition.
What is bicarbonate?
Bicarbonate is an important part of the body's buffering system and helps regulate acid-base balance. It may be reported on blood gases and in other laboratory testing, depending on the clinical setting.
May support an acidic metabolic pattern
Reduced bicarbonate can form part of metabolic acidosis or a compensatory response to some respiratory disturbances.
Interpret in context
A bicarbonate value within the expected range does not exclude respiratory or other clinical problems.
May support an alkaline metabolic pattern
Increased bicarbonate can form part of metabolic alkalosis or compensation for some chronic respiratory disturbances.
How does bicarbonate fit into acid-base balance?
| Value | Broad role | Think |
|---|---|---|
| pH | Shows the overall acid-base direction. | Is the blood relatively acidic or alkaline? |
| PaCO₂ | Represents the respiratory contribution. | Is ventilation affecting the acid-base picture? |
| HCO₃⁻ | Provides important information about the metabolic component. | Is bicarbonate reduced, increased or compensating? |
| Base excess | Helps describe the degree of metabolic disturbance. | Does it support the wider metabolic pattern? |
| Lactate | Can provide additional metabolic and perfusion information. | Is there evidence of significant physiological stress? |
Think pH + CO₂ + bicarbonate
These three values provide a useful starting framework for understanding many acid-base patterns while keeping the patient at the centre of the assessment.
What can reduced bicarbonate indicate?
Low bicarbonate may occur when bicarbonate has been lost or used to buffer an increased acid load. It may also reflect physiological compensation in some respiratory acid-base disturbances.
Acid accumulation
Reduced bicarbonate can support a metabolic acidosis pattern when interpreted with the pH and other values.
Bicarbonate loss
Significant gastrointestinal losses can contribute to low bicarbonate in some clinical situations.
Reduced acid-base regulation
Renal dysfunction can contribute to disturbances in bicarbonate and overall acid-base balance.
What can increased bicarbonate indicate?
Raised bicarbonate may support a metabolic alkalosis pattern or may reflect compensation for a longer-standing respiratory acid-base disturbance.
Loss of gastric acid
Prolonged vomiting is one clinical context associated with metabolic alkalosis.
Fluid and electrolyte changes
Some treatments may contribute to metabolic and electrolyte changes relevant to bicarbonate.
Chronic CO₂ retention
In some longer-standing respiratory conditions, bicarbonate may increase as part of physiological compensation.
Compensation can complicate the picture
This is why blood-gas interpretation requires several values rather than judging a patient's acid-base status from bicarbonate alone.
What should you do with an abnormal bicarbonate result?
Review pH
Establish the overall acid-base direction reported on the blood gas.
Review PaCO₂
Consider whether the respiratory component is contributing to or compensating for the disturbance.
Review bicarbonate
Note whether it is reduced or increased and how this fits with the reported acid-base pattern.
Review related values
Consider base excess, lactate, electrolytes and other relevant laboratory findings.
Assess the patient
Use ABCDE and connect the laboratory result with breathing, circulation, urine output and consciousness.
Escalate deterioration
Significant blood-gas abnormalities or associated physiological deterioration require prompt clinical review.
Never let the blood gas distract you from the patient
Airway
Confirm airway patency and identify immediate threats.
Breathing
Assess respiratory rate, depth, effort, oxygen saturation and changes from baseline.
Circulation
Assess pulse, blood pressure, peripheral perfusion, fluid balance and urine output.
Disability
Assess consciousness and identify confusion, drowsiness or other neurological changes.
Exposure
Consider vomiting, diarrhoea, infection, renal function, medication and other clinical clues.
Escalate
Do not wait for perfect biochemical interpretation before escalating an obviously deteriorating patient.
When should an abnormal bicarbonate increase concern?
- A substantial change from a previous result.
- Low bicarbonate with a worsening metabolic acidosis pattern.
- Raised bicarbonate with significant vomiting or fluid loss.
- Abnormal bicarbonate with worsening pH.
- Associated potassium, sodium or other electrolyte abnormalities.
- Raised lactate or evidence of circulatory compromise.
- New rapid, deep, slow or ineffective breathing.
- Falling blood pressure or urine output.
- New confusion, drowsiness or reduced responsiveness.
Numbers become useful when connected
Bicarbonate has far more meaning when interpreted with pH, carbon dioxide, other laboratory values and changes in the patient's physiology.
Follow the direction of change
Mild abnormality
Bicarbonate is slightly reduced but the patient remains clinically stable.
Result falls further
Repeat testing shows a larger bicarbonate abnormality and the pH is changing.
Patient deteriorates
Respiratory rate rises, blood pressure falls and the patient becomes increasingly drowsy.
Putting bicarbonate into context
Example
A patient with significant acute illness has repeat blood gases during the shift.
Their bicarbonate has fallen further, the pH has decreased and their lactate has increased.
At the bedside their respiratory rate is rising, their blood pressure has fallen and their urine output is decreasing.
The key concern is the combined pattern of worsening metabolic blood-gas findings and physiological deterioration.
As a student nurse, recognise the change, assess using ABCDE within your competence and promptly communicate the trend to the registered and medical team.
Bicarbonate interpretation errors to avoid
- Interpreting bicarbonate without looking at pH.
- Ignoring PaCO₂ and the respiratory component.
- Assuming low bicarbonate always has the same cause.
- Assuming high bicarbonate always means metabolic alkalosis.
- Failing to review base excess, lactate and electrolytes.
- Looking at the blood gas instead of the patient.
- Delaying escalation while trying to fully interpret every value.
Report the blood-gas trend and clinical change
Example escalation
“I'm concerned about Mr Brown. His repeat blood gas has worsened. His bicarbonate and pH have fallen and his lactate has increased. His respiratory rate is rising, his blood pressure is lower and his urine output has reduced.”
This communicates the blood-gas trend and the patient's physiological deterioration rather than simply reporting a bicarbonate result.
Recognise → assess → communicate → escalate
Notice the bicarbonate change
Understand whether bicarbonate is reduced, raised or changing over time.
Connect the values
Consider pH, PaCO₂, base excess, lactate and the patient's ABCDE findings.
Report the pattern
Describe the blood-gas trend alongside the patient's physiological changes and clinical deterioration.
Build your blood-gas interpretation skills
Continue learning how bicarbonate, pH, carbon dioxide, base excess and lactate fit together through the NurseNet Clinical Confidence pathway.
Explore Clinical Confidence →